TROUSSE A FUMEE PYROTECHIQUE PERMETTANT DE PRODUIRE UN ECRAN DE FUMEE

PYROTECHNIC SMOKE KIT FOR GENERATING A SMOKE SCREEN

Abrégé anglais

The pyrotechnic smoke kit for generating a smoke screen
consists of a mixture of a light-metal powder as the metallic
reduction agent, potassium nitrate and, optionally, potassium
perchlorate as the main oxidation agent and at least one
carbonate as an additional auxiliary oxidation agent,
moreover, of substances splitting off nitrogen and at least
one sublimable and/or evaporable non-toxic smoke-forming
substance. A stabilizer from the group of aliphatic and/or
aromatic dicarboxylic acids is added to the mixture of the
smoke kit to stabilize the smoke kit. Due to this, the
formation of gaseous ammonia in the smoke kit can be
prevented.

Revendications

5
What we claim is:
1. A pyrotechnic smoke kit for generating a smoke screen
consisting of a mixture of a light-metal powder as the
metallic reduction agent, potassium nitrate and, optionally,
potassium perchlorate as the main oxidation agent and at least
one carbonate as the additional auxiliary oxidation agent,
moreover of substances splitting off nitrogen and at least one
sublimable and/or evaporable non-toxic smoke-forming
substance, characterized in that a stabilizer from the group
of aliphatic and/or aromatic dicarboxylic acids is added to
the mixture of the smoke kit.
2. The smoke kit according to claim 1, characterized in that
the stabilizer is present in the mixture with a share ranging
from 0.1 to 5% by weight.
3. The smoke kit according to claim 1 or 2, characterized in
that the aliphatic dicarboxylic acids are oxalic acid, malonic
acid, succinic acid, adipic acid or sebacic acid and/or a
mixture of these acids.
4. The smoke kit according to any of the preceding claims,
characterized in that the aromatic dicarboxylic acids are
phthalic acid or terephthalic acid and/or a mixture of these
acids.
5. The smoke kit according to any of the preceding claims,
characterized in that a binding agent from the group of the
halogen-free thermoplastics is additionally added to the
mixture of the smoke kit in order to physically stabilize it.
6. The smoke kit according to claim 5, characterized in that
the binding agent is polyvinyl acetate, polyvinyl alcohol,
polyvinyl butyral, polyvinyl ester or polyvinyl ether.

Description

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CZ1274.en
Pyrotechnic Smoke Kit for Generating a Smoke Screen
The invention relates to a pyrotechnic smoke kit for
generating a smoke screen according to the preamble of claim
1.
Such a pyrotechnic smoke kit is known from DE 3728380 Cl. The
smoke kit is a mixture of a light-metal powder, preferably
magnesium powder as the metallic reduction agent, potassium
nitrate or a mixture of potassium nitrate and potassium
perchlorate as the main oxidation agent, at least one
carbonate, e.g. calcium carbonate, potassium hydrogen
carbonate, sodium hydrogen carbonate, potassium carbonate or
sodium carbonate as a further auxiliary oxidation agent and
substances splitting off nitrogen as combustion moderators and
potassium chloride as sublimable substance and/or common salt
as evaporable non-toxic smoke-forming substance.
Azodicarbonamide, oxamide or dicyandiamide are preferably used
as substances splitting off nitrogen.
The mixture of said substances is preferably pressed into a
casing at whose end an ignition mixture is provided. The
ignition mixture consists substantially of the same components
as the smoke kit, however, with the exception of the
combustion moderators, but has a changed quantitative
composition as this is explained in detail in said patent
specification.
This known pyrotechnic smoke kit proved its excellent worth.
However, it turned out that this mixture is susceptible to
corrosion in the case of very long storage times. The metal
contained in the smoke kit reacts with water that is present
as residual humidity in the smoke kit or originates from the

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environmental humidity, hydrogen being formed. The released
hydrogen reduces the nitrate in the smoke kit to gaseous
ammonia which weakens the structure of a smoke body contained
in the smoke kit already due to the increase in volume
accompanying the formation of gaseous ammonia. After a longer
storage time it may happen that the pyrotechnic smoke kit is
no longer efficient to an optimum degree.
The invention is based on the object of improving the known
smoke kit so that it is efficient to an optimum degree even
after a longer storage time.
According to the invention this object is attained by the
features of claim 1.
Surprisingly, it was found that an admixture of a stabilizer
from the group of the aliphatic and/or aromatic dicarboxylic
acids to the mixture of the smoke kit contributes to a
stabilization of the pyrotechnic smoke kit. Dicarboxylic acids
are acids having two carboxyl groups which have a stabilizing
effect in the mixture of the pyrotechnic smoke kit.
That is to say that solid ammonium salts are formed in the
presence of dicarboxylic acid in the course of a
neutralization. The changes in volume of the smoke kit which
accompany this are clearly less than those in the formation of
gaseous ammonia so that the structure of the smoke kit is not
influenced and the smoke kit as a whole is stabilized.
A low percentage of the dicarboxylic acids must be added to
the mixture of the pyrotechnic smoke kit; this share is
essentially in the range of from 0.1 to 5% by weight.

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Oxalic acid, malonic acid, succinic acid, adipic acid or
sebacic acid and/or a mixture of these substances are/is
preferably used as aliphatic dicarboxylic acids.
Phthalic acid or terephthalic acid or a mixture of these
substances are/is preferably used as aromatic dicarboxylic
acids.
The mentioned aliphatic and/or aromatic dicarboxylic acids
chemically stabilize the mixture of the pyrotechnic smoke kit
so that no ammonia is formed and the mixture of the smoke kit
can be stored for a long period of time without its
operativeness being impaired.
Pyrotechnic smoke kits of the type in question here are
customarily pressed into a casing and covered with an ignition
mixture, which pyrotechnically ignites the smoke kit when it
is used.
In order to physically stabilize the mixture of the smoke kit,
a binding agent may be added to the mixture of the smoke kit
according to the invention, which is selected from the group
of the halogen-free thermoplastics. The binding agent is e.g.
a polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral,
polyvinyl ester or polyvinyl ether.
The mixture for a pyrotechnic smoke kit according to the
invention preferably preferably contains proportionately:
magnesium powder (Mg) as the reduction agent 10-25%
potassium nitrate (KNO3) 20-36%
potassium perchlorate (KC109) 0-15%,

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potassium nitrate and/or potassium perchlorate serving as the
main oxidation agent,
at least one carbonate such as calcium carbonate (CaC03),
potassium hydrogen carbonate (KHCO3), sodium hydrogen carbonate
(NaHCO3), potassium carbonate (K2CO3) and/or sodium carbonate
(Na2CO3) in a share of 12-30%,
the mentioned carbonates serving as further oxidation agents,
potassium chloride (KC1) and/or
common salt (NaCi) as smoke-forming substances 20-50%
aliphatic and/or aromatic
dicarboxylic acids 0.1-5%.
The percentage figures are all in percent by weight.
Azodicarbonamide, oxamide and/or dicyandiamide are preferably
used as substances splitting off nitrogen in a share of 5-20%.
A binding agent from the group of the halogen-free
thermoplastics can still be used for the physical
stabilization of the mixture of the pyrotechnic smoke kit, the
binding agent preferably being polyvinyl acetate, polyvinyl
alcohol, polyvinyl butyral, polyvinyl ester or polyvinyl
ether.